This study is designed 1) to develop a new research tool, the sleep lactate infusion, for studying the panic process, and 2) to exploit this tool to examine the psychophysiological mechanisms involved in panic attacks and to study the relationship between anxiety and activation of brain arousal systems. The relative importance of psychological and biological factors in the sodium lactate induction of panic will be examined. These goals will be achieved by a research design in which the effects of sodium lactate solution administered during sleep and wakefulness to Panic Disorder patients, anxious patients without Panic Disorder, and normal controls are compared. The effect of blockade of panic attacks by pharmacotherapy with imipramine upon the arousal inducing property of sodium lactate will also be studied. Panic Disorder is a relatively common condition, estimated to be prevalent during a single year in the general population at the rate of one per hundred people. This disorder represents a significant health problem because it leads to abuse of tranquilizers, is associated with hypochondriasis and places a burden upon medical facilities, and it severely restricts the lives of many. This study should advance our understanding of the etiology of this disorder and may contribute alternate approaches to treatment.